How to Patch Wall Seems

Make the patch into an access panel or fit a premade access panel, such as ones from Lowe’s made for plumbing.

I used wallpaper rather than paint and it has held up for many years.

You could add a piece of trim right over the seam. When you get done, it would look like a picture frame. You might be able to do something different inside the "frame" to make it look like an actual picture that's suppose to be there, (depending on where its located).

Most campers have a matching trim over the seams. Manufacturers don't even try to install with tight fitting joints. They just stick a matching trim directly on top of the seams and joints in the wall and corners, and ceilings, and floors.

Cut a piece of 1/4" plywood slightly larger than the hole and stain it to look nice. Or use something like a cold air return grill or floor register.
https://www.amazon.com/slp/cold-air-return-vents/kaebekqjqdgy7ew

DutchmenSport wrote:
Caulking would work. But I'd probably use Liquid Nails. You need something that dries like a hard rubber. It will still have flexibility when dry, but not so stiff it will crack and break at the first sign of a flex.

The only problem with Liquid Nails, you've got to get it completely right while it's still wet (smoothed out and even), because once it's dry, it doesn't sand very nice at all.

Depending on how big the holes are (if small like nail holes from hanging a picture), then even a silicon calk would work ok. If the holes are bigger (like a quarter or half dollar size or bigger, then you need to figure a way to put a backing on it first, then fill the hole from the front, smooth, and paint.

Sorry for the confusion. When I say "hole" I mean a seam. What I did was cut a square into a panel to reinforce water damage and fix leaks. I am now cutting a square piece to patch it but am not sure what to use to fill the seam around it.

Caulking would work. But I'd probably use Liquid Nails. You need something that dries like a hard rubber. It will still have flexibility when dry, but not so stiff it will crack and break at the first sign of a flex.

The only problem with Liquid Nails, you've got to get it completely right while it's still wet (smoothed out and even), because once it's dry, it doesn't sand very nice at all.

Depending on how big the holes are (if small like nail holes from hanging a picture), then even a silicon calk would work ok. If the holes are bigger (like a quarter or half dollar size or bigger, then you need to figure a way to put a backing on it first, then fill the hole from the front, smooth, and paint.